1. Field of the Invention
The present invention relates to a technique for improving an exhaust pipe structure of a vehicle with a low floor.
2. Description of the Related Art
Various techniques are used for mounting a power unit below a body frame in a vehicle with a low floor, such as a scooter-type motorcycle or a scooter-type three-wheeled vehicle. For example, Japanese published unexamined patent application No. 2001-88763 (see FIG. 2 on pp. 3 and 4) discloses such a technique.
Referring to FIG. 28, the outline of a conventional type low floor type vehicle as disclosed in patent application No. 2001-88763 is described below. FIG. 28 is a schematic diagram showing the conventional low floor type vehicle of Japanese published unexamined patent application No. 2001-88763. A conventional low floor type vehicle 300 is a scooter type motorcycle in which a power unit 320 is mounted in a double cradle type body frame under 310 and under a low floor 318.
The body frame 310 is composed of a pair of right and left upper frames 312, 312 (only the left upper frame is shown and it is similar to the right upper frame for the following components) extended backward and downward from a head pipe 311, a pair of right and left down frames 313, 313 extended downward from the head pipe 311, a pair of right and left center frames 314, 314 extended backward and upward from the down frames 313, 313, a pair of right and left lower frames 315, 315 extended backward from each lower end of the down frames 313, 313 and a pair of right and left rear frames 316, 316 each of which connects each rear end of the lower frames 315, 315 and each rear end of the center frames 314, 314.
Each rear end of the upper frames 312, 312 is connected to each extension of the center frames 314, 314. The low floor 318 can be supported by the body frame 310. The low floor 318 is a floor for bearing the feet of a rider.
The power unit 320 is composed of a front longitudinal V-type engine 321 and a rear transmission unit 331. The V-type engine 321 is a water-cooled engine provided with a front cylinder 322 and a rear cylinder 323 so that a banking angle θ10 (an angle θ10 between the cylinders 322 and 323) of approximately 45° is formed when the engine is viewed from the side. The front cylinder 322 is extended substantially horizontally forward. The rear cylinder 323 is extended toward the head pipe 311. As a result, the banking angle θ10 is approximately 45° when the engine is viewed from the side. Naturally, a bisector L11 of the banking angle θ10 passes between the head pipe 311 and a front wheel 351. A reference number 324 denotes a crankshaft.
Each exhaust pipe 326, 326 connected to each cylinder 322, 323 is extended backward under the engine 321 and reaches a muffler 327.
Further, in the low floor type vehicle 300, an air cleaner 340 is arranged in a space between the head pipe 311 and the rear cylinder 323, a radiator for cooling the engine 352 is arranged between the engine 321 and the front wheel 351, a seat 353 is arranged on the upside of the rear, and a front fuel tank 354 and a rear housing box 355 are arranged under the seat 353.
The transmission unit 331 is provided with a transmission device 333 which can be vertically swung with a final output shaft 332 as the base of a swing. A rear wheel 334 is attached to the transmission device 333 and the transmission device 333 can be suspended from the body frame 310 via a rear cushion 335. The rear cushion 335 is vertically arranged under the seat 353 and between the fuel tank 354 and the housing box 355. L12 denotes a straight line passing the head pipe 311 and the final output shaft 332.
The air cleaner 340 is provided with a filter element 341 inside, and an intake port 342 on the upside. The intake port 342 is covered with an upper lid 343. Each cylinder 322, 323 is connected to such an air cleaner 340 via each intake coupling pipe 344, 345. The intake coupling pipe 344 connected to the front cylinder 322 reaches the air cleaner 340 through space between the cylinders 322 and 323. In the meantime, the intake coupling pipe 345 connected to the rear cylinder 323 reaches the air cleaner 340 through space above the rear cylinder 323.
However, in the conventional low floor type vehicle 300, the two exhaust pipes 326, 326 are extended backward below the engine 321 from the front of the longitudinal V-type engine 321. Therefore, space for the two exhaust pipes is required to be secured in the same position and the degree of freedom in design is low.
In addition, if the banking angle θ 10 of the longitudinal V-type engine 321 is increased, space for equalizing the length of the two exhaust pipes 326, 326 in consideration of exhaust performance is further required.